We have continued to explore the role that reactive oxygen species (ROS) play in signal transduction pathways. We have previously shown that a variety of growth factors and cytokines induce the generation of ROS following ligand binding. Our studies suggest that the pathway leading to ROS generation involves the activation of the small GTP-binding proteins Rac1 as well as Ras proteins. This has led us to explore the role of this family of GTPases in redox regulation. We have also explored the role that ROS play in apoptosis, and more recently in replicative senescence and aging. In the previous year we have been able to demonstrate that oxidants function as specific regulators of pathways linked to aging. In particular, we have demonstrated a relationship between forkhead proteins, a gene family that regulates longevity in C. elegans, p66shc one of the few genes known to regulate longevity in mammalian cells, and intracellular ROS, thought to regulate aging across a diverse number of species. These studies were published in journal Science and provided a mechanistic link between oxidant signal transduction and gene products linked to longevity. We are continuing to pursue these observations and have recently implicated p66shc in mitochondrial oxygen consumption. This provides further mechanistic insight into how p66shc might regulate life span and suggests a convergence of signal transduction with mitochondrial metabolism. These studies involving oxidants and aging have led us to begin to pursue the various signal transduction pathways that regulate metabolism in the cell. We are particularly interested in how the cell chooses between mitochondrial and non-mitochondrial ATP generation. We believe that such choices might be governed by the intracellular redox state of the cell. Ultimately, we believe this regulation may relate to the role that oxidants have in a variety of disease states as well as in normal aging. These metabolic studies involve a variety of experimental systems ranging from the simple organism C.elegans to more complex mammalian systems. Finally, we are also directly assessing the in vivo role of a number of classic oxidases. Studies are now underway to genetically disrupt the xanthine dehydrogenase gene to further understand the role of this oxidase in normal and pathophysiological conditions. We believe that this gene product may be involved in regulating blood pressure as well as regulating tissue damage secondary to conditions such as myocardial infarction or stroke.